﻿142 C. D. Walcott — Cambrian System of North America. 



Olenellus or Middle Cambrian fauna, located its upper horizon 

 and ascertained that the entire Upper Cambrian was absent by 

 non-deposition, the Silurian resting conformably on strata of Mid- 

 The section at the base rests on granite near 



die Cambrian age. 



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the mouth of Big Cottonwood Canon, and the strata continue up 

 the canon in an unbroken, conformable series of siliceous rock, 

 shales, quartzites and sandstones, until 12,000 feet in thickness 



